DESCRIPTION (Adapted from Applicant's Description): Nearly half of peak bone mass (PBM) is acquired during adolescence, making this a critical period to foster bone mineral gains. While genetic factors explain much of the variation in PBM, it is estimated that lifestyle factors can explain up to 40% of the variation. The primary aim of this proposal is to measure the relative contributions of controllable lifestyle factors: intakes of nutrients and supplements, restrained eating practices, physical activity behaviors, smoking behavior, reproductive and contraceptive practices in early, mid and late adolescence, while controlling for genetics, menarcheal age, body composition and weight. Current knowledge of adolescent bone mineral acquisition has been limited by studies with too few subjects or inadequate duration to allow comparison of the effects of behavior at various stages of adolescence on peak bone mass and by the paucity of studies with significant numbers of minority women. This study will avoid these limitations in a cost-effective manner by taking advantage of an extensive and current database on 700 black and white 20-21 year old women followed longitudinally for 10 years in the NHLBI Growth and Health Study (NGHS). Dual energy x-ray absorptiometry (DXA) measurements will be made to assess bone mineral content (BMC), bone mineral density (BMD, BMAD), and bone geometry (hip axis length). Calcaneous ultrasound data will provide additional information on the internal architecture of the bone. Data will also be gathered on vitamin D receptor genotype and current behaviors associated with bone mineral acquisition. A historical cohort design will be employed to provide extensive annual lifestyle data prospectively collected beginning at age 9 years. The study promises to reveal relationships between genetic and lifestyle factors in early, mid and late adolescence and to provide much needed information on the impacts of childhood and adolescent behaviors on skeletal health.